Research on the Technical Scheme for Conversion of 500kV Submarine SCLF AC Cable Circuit to DC Operation in Hainan Grid-connection Project

摘要

The first AC 500 kV submarine cable circuit in China was put into operation on June 2009. In order to increase the transmission capacity, it is under consideration to convert this kraft paper insulated SCLF cable circuit from AC to DC operation. From the existing single circuit AC cable line, two circuits can be arranged under DC operation, one bipolar and one monopolar. The bipolar circuit consists of two cables, a DC plus pole and a DC minus pole. The monopolar circuit consists of only one cable. According to the cable structure and circuit grounding mode, return current will flow through the coaxial metal layers of the cable as well as the seawater and earth. The long term operation voltage is to be designed as 500 kV based on the insulation withstand levels of DC voltage, polarity reversal voltage and DC superimposed impulse voltage. The permissible load current is determined as 1150 A and 1000 A using the calculation method recommended by IEC60287 for different current return modes. Under the designed DC operation scheme, the transmission capacity will be 2.5 times more than the existing AC. The follow-up testing and checking work is underway.